Example of the DIA method applied to 67P. This frame is taken from the October 2007 data set, and shows the original (left) and subtracted (right) versions of the same area, centred on the comet position. The comet is impossible to identify, much less perform photometry on, in such a crowded field, but is clearly revealed as a positive and negative pair in the subtracted frames. Saturated stars are masked in the difference image. North is up, East to the left.